In the past, there has been extensive description in the patent and other technical literature of electrophoretic migration imaging processes. For example, a description of such processes may be found in U.S. Pat. Nos. 2,758,939 by Sugarman issued Aug. 14, 1956; 2,940,847; 3,100,426; 3,140,175 and 3,143,508, all by Kaprelian; 3,384,565; 3,384,488 and 3,615,558, all by Tulagin et al.; 3,384,566 by Clark; and 3,383,993 by Yeh. In addition to the foregoing patent literature directed to conventional photoelectrophoretic migration imaging processes, another type of photoelectrophoretic migration imaging process which advantageously provides for image reversal is described in Groner, U.S. Pat. No. 3,976,485 issued Aug. 24, 1976.
In general, each of the foregoing electrophoretic migration imaging processes typically employs a layer of electrical charge-bearing photoconductive particles, i.e., electrically photosensitive particles, positioned between two spaced electrodes, one of which may be transparent. To achieve image formation in these processes, the charge-bearing photosensitive particles positioned between the two spaced electrodes, as described above, are subjected to the influence of an electric field and exposed to activating radiation. As a result, the charge-bearing electrically photosensitive particles are caused to migrate electrophoretically to the surface of one or the other of the spaced electrodes, and one obtains an image pattern on the surface of these electrodes. Typically, a negative image is formed on one electrode, and a positive image is formed on the opposite electrode. Image discrimination occurs in the various electrophoretic migration imaging processes as a result of a net change in charge polarity of either the exposed electrically photosensitive particles (in the case of conventional electrophoretic migration imaging) or the unexposed electrically photosensitive particles (in the case of the electrophoretic migration imaging process described in the above-noted Groner patent application) so that the image formed on one electrode surface is composed ideally of electrically photosensitive particles of one charge polarity, either negative or positive polarity, and the image formed on the opposite polarity electrode surface is composed ideally of electrically photosensitive particles having the opposite charge polarity, either positive or negative.
In any case, regardless of the particular electrophoretic migration imaging process employed, it is apparent that an essential component of any such process is the electrically photosensitive particles. And, of course, to obtain an easy-to-read, visible image it is important that these electrically photosensitive particles be colored, as well as electrically photosensitive. Accordingly, as is apparent from the technical literature regarding electrophoretic migration imaging processes, work has been carried on in the past and is continuing, to find particles which possess both useful levels of electrical photosensitivity and which exhibit good colorant properties. Thus, for example, various types of electrically photosensitive materials are disclosed for use in electrophoretic migration imaging processes, for example, in U.S. Pat. Nos. 2,758,939 by Sugarman, 2,940,847 by Kaprelian, and 3,384,488; 3,474,020 and 3,615,558 by Tulagin et al., noted hereinabove.
Yellow electrically photosensitive materials are useful in migration imaging processes. Such materials are particularly useful in photoelectrophoretic polychrome migration imaging processes based on a subtractive multicolor system. However, yellow electrically photosensitive materials disclosed in the prior art have been considered unsatisfactory for one reason or another. For an example the widely used Indofast yellow results in the formation of polychrome images in which the rendition of reds and greens is less than desired. There is a need for a yellow electrically photosensitive material which form better images in photoelectrophoretic imaging processes.